Tuesday, January 19, 2010

HT Saver

One of my ham radio pet hates are those SMA sockets used to mount the antennas on all modern VHF/UHF handheld radios. They are very fragile, and not designed for the repeated changing of antennas that most of us go in for. I don't see any justification for using them except on those very slim credit card sized handhelds which are pretty fragile devices anyway. But all the manufacturers now use them so we're stuck with them.

With the Kenwood TH-F6A / TH-F7E you really have no choice to switch antennas if you want to make use of the shortwave receive capability because the VHF/UHF antennas are useless on shortwave. Last week I made a shortwave receive antenna for it which I called the Wonder Whip. This antenna works on 2m and 70cm transmit as well, but it is a bit long to leave on the radio when carrying it so I still need to remove it quite frequently.

I made the Wonder Whip on a BNC connector so I needed to use a BNC to SMA adapter to use it on the radio. The trouble with the readily obtainable BNC to SMA adapters is that they do not have a large base that clamps down on to the body of the radio for extra support like the supplied antenna does. This means the SMA adapter takes the full force of any sideways knocks. It is very easy to snap off, as many HT owners have found to their cost. So when I saw some SMA to BNC adapters with a large base being sold very cheaply on eBay by a Hong Kong trader called PartsPipe I ordered a couple of them. The pair cost less than £5 including postage and they arrived in just over a week which is one of the quickest shipments I've had from the Far East.

To my disappointment I found that when screwed on to the TH-F7E as far as it would go there was a gap of about one millimetre between the base of the adapter and the radio. Fortunately I found a steel washer that slips over the SMA antenna connector and fills the gap. I will probably be able to get a matching brass washer at a local DIY store but the steel one will do for the moment. Now any BNC antennas will be fully supported by the body of the radio.

If I use only BNC base antennas from now on I can leave the adapter permanently in place and will not have to keep connecting and removing things from the SMA socket, which I think is rated for only something like 100 connections. I think this is a much better solution: BNC connectors are more robust and in the unlikely event you do get a problem you can just replace the inexpensive adapter - which is why I got two of them!

Now I just have to decide what to do with my arsenal of SMA-based antennas. Probably flog them on eBay!